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Particles as waves and Light as particles

Particles as waves and Light as particles. Chapter 6 part II. Energy is Quantized. Energy can only occur in discrete units of size hv. Each packet is called a quantum. Energy can only be transferred in whole quanta. Energy seems to have particle like behavior. Photons.

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Particles as waves and Light as particles

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  1. Particles as waves and Light as particles Chapter 6 part II

  2. Energy is Quantized • Energy can only occur in discrete units of size hv. • Each packet is called a quantum. • Energy can only be transferred in whole quanta. • Energy seems to have particle like behavior.

  3. Photons • Einstein proposed that electromagnetic radiation is quantized. • This light can be viewed as a stream of particles. • Each particle is a photon, with energy of: • Ephoton=hv=hc/

  4. Theory of Relativity • Einstein went on to propose this: • E=mc2 • Energy has mass!!!

  5. If E=mc2 and E=hc/…Then • m = (E/c2) • Ephoton = hc  • Substitute hc for E  • Then m= (E/c2) = (hc/ ) = h c2 c • This means that a photon appears to have mass!

  6. The dual nature of light • Compton working with x-rays and electrons seems to have proved this. • Energy is quantized. • Electromagnetic radiation once thought to act only as waves, seems to also have the characteristics of particles. • Can matter have wave-like characteristics?

  7. Louis de Broglie • de Broglie solved the problem of the wavelike behavior of a particle. • Then m= h (velocity v) • Then solving for  we get h mv • This is called de Broglie’s equation.

  8. For example: • Compare the wavelength of an electron (m=9.11x10-31kg) traveling at a speed of 1.0x107m/s with that of a baseball (m=0.10kg) traveling at 35 m/s

  9. Answer: • =h/ mv • h= 6.626 x 10-34 Js • 1 J= 1kg m2/s2 • For electron = 6.626 x 10-34 (kgmm)/s (9.11x10-31 kg)(1.0x107m/s) Answer: 7.27 x 10-11m

  10. And the Ball?? • 1.9x10-34m

  11. Atomic Spectrum of Hydrogen • When light is passed through a prism one gets an emission spectrum. • When all wavelengths are possible one gets a continuous spectrum. • When energy is quantized the spectrum is a line spectrum, or discrete.

  12. Light & Electromagnetic Radiation • The light spectrum is continuous. • All the wavelengths of light may pass.

  13. The hydrogen emission spectrum: • Is discrete. • This indicates only certain energies are allowed for the electron in the hydrogen atom.

  14. Hydrogen is discrete as the energy of electrons are quantized. • ∆E =hv= hc/  •  is the wavelength of light emitted. • Since the line is discrete only certain energies are possible for the hydrogen electron.

  15. The Bohr model: • Bohr’s quantum model proposed that electrons in a hydrogen atom move around the nucleus in certain allowed circular orbits.

  16. Bohr’s equation • Z is the nuclear charge • n is an integer representing the orbital, larger n= larger radius • n=1 is the ground state

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